There are many known processes for joining or uniting metallic sheets in an overlapping fashion including spot welding, tongue and groove type fittings, inserting a metallic locking-core into channels formed in the overlapping sheet material, using rivets, and the like in forming metallic boxes, housings and electrical or heat shields. Some of these methods and the resulting box or rectangular housing structures are shown in the following U.S. Pat. Nos.: Bianca et al 2,815,568; Pfister et al 2,916,181; Oetiker 3,286,314; Coop 3,824,757; Krantz 1,557,066; Walter et al 4,550,479; Pfistershammer 2,663,072; Cooley 2,426,670; Dieckmann 597,056; Plecker 518,767 and Brown et al 454,636. In general, the mechanical crimping methods of the prior art in the formation of a lap joint or seam between two overlapping sheet metal ends has been a simple mechanical crimp, formed in a separate secondary operation, forcing an end of one overlapping metal sheet portion under an end or aperture in the other sheet metal portion to form a mechanical interlock suitable for most purposes. This type of mechanical interlock, for example, is shown in the above-identified Bianca et al, Pfister et al, Oetiker and Coop patents.
Spot welding, used for many years in producing electrical shields in a rectangular sheet metal box type structure having one or more open ends is a much more expensive process than mechanical crimping due to the additional labor, machinery and time necessary for an extra, secondary process step and station for each housing or shield. However, prior to the present invention, it was felt that spot welding was necessary in order to produce an electrical shield or other housing structure having sufficient joint or seam strength to maintain the structural integrity of the seam or joint. Spot welding, however, generally secures overlapping sheet metal portions only in the area of spot welding and cannot produce a seam wherein the overlapping sheet metal portions are in direct contact over essentially 100% of the surface area of the overlapping sheet metal portions.
The above disadvantages in spot welding and other mechanically crimped seams of the prior art have been overcome in accordance with the principles of the present invention.